The invention concerns a double screen former for the manufacture of a fiber material web, specifically a paper web, from a fiber material suspension.
The invention is based on the object of the yet unpublished German patent application P 3927597.3. Each of the flexibly supported laths is arranged there opposite a gap between two rigid laths. There are approximately as many rigid laths provided as there are flexible ones, so that a zigzag arrangement of the laths comes about. The spacing between the laths is relatively large, namely, about five times as great as the thickness of the laths. What is to be accomplished with these relatively large spaces (compared to the object of DE OS 3823966) is an easier removal of the water proceeding through the wire meshes. This applies, for instance with a horizontal extension of the screen, primarily to the laths contained in the bottom screen loop. In the case of relatively small spaces between the laths, clogging had occasionally occurred there, for instance through deposition of slime substances between the laths.
On the other hand, one of the advantages of the prior double screen former is that fiber material webs with a relatively good formation can be formed; i.e., a very beautiful, uniform fiber distribution is accomplished in the finished fiber material web, for instance in the paper web.
Difficulties have occurred, however, in that due to the changeover to larger spaces between the laths, the results regarding the formation are no longer fully satisfactory.
Therefore, the problem underlying the invention is to advance the double screen former so that both requirements will be met, namely on the one hand a maximally good formation of the formed fiber material web, and on the other hand the elimination of the risk of depositions between the laths.